This invention relates to a marine riser system having flexible flowlines. In particular, it relates to apparatus for connecting a surface facility to a subsea wellhead or gathering system.
In the production of fluid hydrocarbons from deepwater marine oil and gas deposits, a fluid communication system from the marine bottom to the surface after production is required. Such a system, commonly called a production riser, usually includes multiple conduits through which various produced fluids are transported to and from the surface, including oil and gas production lines, service and hydraulic control lines.
In many offshore production areas, a floating vessel can be used as a production and/or storage facility. Since the facility is exposed to surface and sub-surface conditions, it undergoes a variety of movements. In such a zone of turbulence, heave, roll, pitch, drift, etc., may be caused by surface and near surface conditions. In order for a production riser system to function adequately with such a facility, it must be sufficiently compliant to compensate for such movements over long periods of operation without failure.
Such a marine riser is disclosed in U.S. Pat. No. 4,182,584. This compliant riser system includes (1) a lower section which extends from the marine bottom to a fixed position just below the zone of turbulence that exists near the surface of the water, and (2) an upper flexible section which is comprised of flexible flowlines that extend from the top of the rigid section, through the turbulent zone, to a floating vessel on the surface. A submerged buoy is attached to the top of the rigid section to maintain the rigid section in a substantially vertical position within the water.